The invention relates to a machine tool for at least partial machining, contour-dependent cutting, or milling of a clampable part made from a plate-shaped workpiece, having a suction apparatus, provided for engaging the back side or lower side of the workpiece, that acts as a clamping device and that has individual suction devices which can in particular be situated in displaceable fashion on a machine frame of the machine.
Machines of this sort are known in many forms. The clamping of the workpiece in such machines takes place using a suction apparatus that can engage on the back side or lower side of the workpiece, which has the advantage that this suction apparatus can be adjusted or displaced according to the shape of the workpiece. In addition, the edges of the workpiece remain free, so that they are easily accessible and can be reached correspondingly well and machined using a tool. Even profilings, or recesses to be made in the narrow side of a plate-shaped workpiece, can be machined.
However, in many cases workpieces must be machined from a material that is air permeable. Moreover, such workpieces, especially if they are made of wood, can be warped or have faults and then cannot be grasped in the area of individual suction devices of the suction apparatus so that the workpiece can be displaced or even entirely torn away during the machining. Besides the resulting spoilage, this also presents a risk to the user.
If, for example, relatively thin workpieces having the same contour are to be manufactured, they can be deformed by the suction apparatus and its individual suction devices. Moreover, it is time-consuming if a plurality of identical individual pieces having the same contour must be produced one after the other on the same machine.
The object therefore arises of creating a machine of the type named above that retains the advantages of a fastening of the workpiece using suction apparatuses that leave a workpiece surface entirely free, but in which it is also possible to machine workpieces that are made of an air permeable material and/or that have warped or deformed or similar uneven sections.
In order to achieve this apparently self-contradictory goal, it is provided that the machine has as a second clamping device that is used to apply pressure to the side of the workpiece facing away from the suction device as a hold-down device, and that the hold-down device has, on its contact region that applies pressure to the workpiece, at least one or two pressure rollers at a distance from one another, and the hold-down device can, under pressure, be displaced relative to the workpiece, transversely to the axis of the pressure roller, and that the hold-down device can be displaced synchronously with a tool that is used for the machining of the workpiece.
Surprisingly, the machine tool according to the present invention is thus outfitted with two clamping devices of different types, namely with the already-mentioned suction apparatus and additionally with the hold-down device, which likewise acts as a clamping device. In this way, it is possible to clamp even workpieces that cannot be suctioned because they let too much air through, or that have warped or uneven spots that cannot be grasped uniformly at all suction heads or suction points. Moreover, it is possible for workpieces having congruent contours to be clamped simultaneously as a stack, with the aid of the hold-down device, and then machined. If necessary, here the clamping can additionally be supported by the suction apparatus, which additionally grasps at least the lowest workpiece of such a stack.
The user thus has the possibility, optionally and according to the requirements of the edge contour that is to be manufactured, etc., of fixing the workpiece using the suction device, or using the hold-down device, or, in particular cases, using both clamping devices. In this way, the apparent excess expense in equipment is compensated in that a further machine tool is not required for workpieces that cannot be clamped with sufficient stability using a suction device.
Because the hold-down device, at its contact region that applies pressure to the workpiece, has at least one or two pressure rollers set at a distance from one another, and can be displaced, under pressure, relative to the workpiece, transversely to the axis of the pressure rollers, the rollers can roll on the surface of the tool. This allows the hold-down device to optionally be used on the workpiece at the points at which correspondingly large forces, coming in particular from the tool, are to be received. Here, due to the synchronous displaceability, the clamping point formed by this pressure roller or pressure rollers can migrate together with the tool, with its machining advance, and can always act at the point at which the machining forces occur.
A particularly useful preferred embodiment of the invention is provided in that the at least two pressure rollers of the hold-down device are situated parallel to one another, and at a distance from one another, and are connected with an advancement device or feeder for the tool. In this way, the synchronous movement of the hold-down device and of the tool is achieved automatically, and can be brought about using a single drive.
The tool, in particular a milling cutter, can be situated in the intermediate space between the two pressure rollers, and the advance device for the displacement of the tool can also be used for the displacement of the pressure rollers of the hold-down device. In this way, the respective machining point on the workpiece is clamped fast particularly reliably, because the holding down takes place on both sides of the tool, immediately adjacent thereto. This arrangement can correspond approximately to that known from DE 27 26 382 C3, and can have an analogous manner of operation.
The suction apparatus can have at least one, or preferably a plurality, of suction consoles, on which individual suction devices are situated detachably and removably, as well as adjustably, and an exchangeable base plate can be provided as support for a workpiece, with the base plate fitting onto the suction console and acting thereon as a support for workpieces that can be clamped using the hold-down device. The user can thus remove the suction heads, and can create a stable support with the aid of a base plate for workpieces that during their machining are to be pressed with great force onto a surface that is as flat as possible. However, it is also possible to apply a workpiece immediately onto the suction heads, and to hold it (or hold it additionally) with the hold-down device.
In an especially advantageous embodiment of the present invention, and therefore worthy of independent protection, a stop rail can be situated on at least one edge of the machining or bearing surface for the workpiece, and this rail can be moved away from its stop position so as to expose the edge of a workpiece previously aligned thereon. Thus, a user can orient a workpiece, for example a plate of wood, or also plates of wood situated one on top of the other with the aid of this stop rail, as is also often customarily done in other cases of wood machining in particular, after which the workpiece is then clamped. If the edge of this workpiece with which the workpiece has been applied to the stop rail is to be machined, this edge can also be machined in unhindered fashion after the rail has been moved away.
Here, it is particularly advantageous if the stop rail extends over the entire dimension of one side of the working surface, and in particular has on at least one end an additional stop or sliding stop that protrudes at a right angle to the orientation thereof, and that can be displaced and fixed in the longitudinal direction of the stop rail if necessary. In this way, in particular rectangular workpieces can be properly aligned, because they can be applied to the stop rail and to an additional stop not only with one edge, but also with an edge at a right angle thereto, and in this way can be aligned.
The stop rail can be fastened to swivel arms that can in particular be swiveled approximately in a plane situated parallel to the working surface, or that is in accordance with the working surface. The stop rail could also for example be swiveled behind or under the working surface from its position of use, but often there is no space there, so that a swiveling that takes place approximately in the plane of the working surface is also advantageous for reasons of space. If necessary, such a swiveling arrangement can also be used for the displacement of the stop element position.
Swivel arms can engage on the stop element that are situated parallel to one another and can be swiveled synchronously, about their swivel axis, at a distance from the stop rail, by drive arms that are situated parallel to one another and offset in relation to the swivel arms by an angular distance, on which there engages a rotational drive or, if necessary a connecting rod and a drive. Using a plurality of swivel arms, preferably two, a relatively long rail can be swiveled practically parallel to itself from the position of use into an idle position. Here, the drive arms can be situated at an angle to the respective swivel arm in order to have a position relative to a drive that is as advantageous as possible.
It is also particularly advantageous for the acceptance of contact forces if, in the position of use of the stop rail, the swivel arms are situated at a right angle to this rail and the actuating arms are situated so as to be displaced thereto by an acute angle, for example by approximately 45xc2x0, so that a swiveling of the drive arms by 90xc2x0 brings the swivel arms and the stop rail into accordance with one another. In this way, the arrangement has a relatively low space requirement.